This invention relates generally to optical networks. More particularly, the present invention relates to ultra-fast optical switches within an optical network.
In recent years, the exponential growth in computing power has been paralleled with an explosion in demand for communication bandwidth. One key element of this bandwidth explosion has been optical wave guides or optical fiber links, which have enabled bit rates far higher than were possible using conventional copper cables.
To achieve high bit rates, optical switches are used in many conventional optical networks. Conventional switches typically rely on electronic cores, which convert optical signals to electronic signals. Electronic circuits and the switch core then direct the electronic signals to a desired output port. A final electrical-to-optical conversion is performed to transform the signal back into light for propagation of the optical signal along the optical wave guides of a network. One major problem with electronic circuits used for switching is that they do not scale well to large port counts and are costly to replace for network upgrades to support higher data rates needed for the growing demand for bandwidth.
Microelectromechanical systems (MEMS) can substantially reduce or eliminate the problems associated with electronic circuits. MEMS technology comprises complex machines so small that the systems are typically measured in microns. MEMS devices typically combine electronic circuitry with mechanical structures to perform specific tasks. For optical switches, the key mechanical components are MEMS-based micro-machined mirrors fabricated on silicon chips using well established, varied-large-scale integration (VLSI) complimentary metal-oxide semiconductor (CMOS) foundry processes. These processes can include, but are not limited to, photolithography, material deposition, and chemical etching.
Because of the reliability and extremely compact design of MEMS optical switching devices, these devices can be integrated easily into a variety of systems such as instrumentation and communication applications. Instrumentation applications include, but are not limited to, air bag sensors, pressure sensors, displays, adaptive optics, scanners, printers, data storage and micro-fluidics. Communication applications include, but are not limited to, packet switching, optical cross connect (OXC), optical add-drop multiplexers (OADMs), optical network protection, and optical network restoration. Specific applications for OADMs include: linear add-drop for backbone dense wave division multiplexing (DWDM) networks, hubbed rings and metro access networks, and logical mesh rings that allow dynamic path reconfiguration based on bandwidth across a network.
In addition to the general MEMS optical switching device applications noted above, there are also specific MEMS optical switch device applications. For example, at least two specific MEMS optical switching designs exist today: the (a) two-dimensional (2-D) or digital approach and (b) three-dimensional (3-D) or analog approach (2N architecture). Both optical switching architectures operate on a few basic principles: an MEMS optical switch routes optical signals from one optical wave guide to another. The routing can be accomplished by steering the light, reflecting the light off a moveable mirror, and redirecting the light back into one of N possible output ports.
While the operating principles of MEMS optical switching devices may appear to be simple, problems exist with conventional MEMS optical switching devices because of the need for precision control of a moveable optical element in a high speed environment. In other words, conventional MEMS optical switching devices lack precise and controlled movement of mirrors used to reflect optical signals originating from one optical wave guide and transmitted to another optical wave guide.
This lack of precise and controlled movement of the optical element in a MEMS optical switching device can be attributed to the low forces that are used to move the optical element. Typically, conventional MEMS optical switches utilize electrostatic methods to induce movement of an optical element. Electrostatic methods rely on the attraction of oppositely charged mechanical elements. Conventional optical switches typically use a single electrode to pull a structure having an electrical charge of opposite sign to the electrode.
Single electrode actuators do not provide for precise and controlled movement of the deflecting or moving structure. For optical switch applications in which it is desirable to merely rotate the optical element or mirror, the single electrode actuation usually produces a moment and a force. When a moment and a force is produced, translational movement of the deflecting structure is produced. This translational movement is undesirable when the optical element or mirror is designed to be simply rotated about an axis.
Accordingly, there is a need in the art for an optical switching device that generates pure moments to move or rotate a respective optical element such as a mirror. A further need in the art exists for an optical switching device that can produce moments for rotating a respective optical element with increased precision and control as well as increased repeatability. Another need exists in the art for an optical switching device that can also increase the speed and precision at which optical signals are switched within an optical network. Another need exists in the art for an optical switching device that operates with uniformly low insertion loss, low operating power, and less than millisecond switching time. A further need exists in the art for an optical switching device that provides for uniform optical element positioning and registration, as well as resistance to shock and vibration. Another need exists in the art for an optical switching device that can be produced in high volumes by utilizing proven semiconductor process technology. And lastly another need exists in the art for an optical switching device that can support widely varying data rates, modulation formats, and optical signal wave lengths.
The present invention solves the problems of conventional optical networks by providing an optical switching device that can increase the speed and precision at which optical signals are switched within an optical network. The present invention can comprise a system of one or more optical switching devices. Each optical switching device can achieve relatively high switching speeds such as between thirty (30) nano-seconds to fifty (50) nano-seconds or lower than thirty nano-second speeds with precise angular movement. The switching speed can be defined as the movement of an optical element from a first switching position to a second switching position. A switching position can be defined as a position in which electrodes are applying a voltage to maintain membrane supports and an optical element at a predefined location. The relatively high switching speeds and precise angular movement of the optical element can be attributed to utilizing a combination of electrodes and membrane supports made from predefined materials that react to the electrodes.
More specifically, the optical switching device can comprise a optical element, one or more membrane supports which carry the optical element, and upper and lower electrodes that control the deflection of the one or more membrane supports. The optical switching device can comprise a microelectromechanical system (MEMS) device that can be fabricated by the adding or etching layers of materials such as in photolithography manufacturing techniques. The optical element can comprise a mirror made from reflective materials such as a layer of gold. The membrane supports can comprise planar strips fabricated from thin layered materials such as silicon nitride (Si3N4). And the upper and lower electrodes can be electrical conductors made from materials such as titanium nitride (TiN).
Because of the materials used for the membrane supports, the membrane supports can be manufactured with relatively high tensile stresses. A membrane support with high stresses can be easily stabilized and is thus suitable for supporting an optical element which is formed on a respective surface of a membrane support. Further, a membrane support with high stresses typically has increased stiffness so that it can provide rapid reaction of the optical element. The optical element typically moves in unison with the membrane support since it is usually firmly attached to the membrane support and because the membrane support has sufficient stiffness such that the optical element will not lag behind any movement of the membrane support. The stiffness of the membrane support can also reduce or prevent low modes of vibration from occurring in the optical element after moving the optical element to a switching position.
In addition to providing membrane supports with high stresses, the present invention can also provide a method and system for switching optical signals that employs multiple forces, as opposed to a single force, to move the optical element into a switching position. More specifically, the present invention employs substantially pure moments to rotate the membrane supports and the optical element from a rest position to a switching direction. The substantially pure moments can be generated by activating opposing upper and lower electrodes that deflect individual membrane supports of respective pairs of membrane supports. In this way, undesirable translational movement of the membrane supports and optical element can be substantially reduced or eliminated, which, in turn, increases the precision of the angular movement of the membrane supports and optical element.
According to another aspect of the present invention, a plurality of optical switching devices may be provided on a single planar surface to form a planar array of optical switching devices having multiple columns. More specifically, a plurality of optical switching devices can be aligned into an linear array. Each optical switching device of the linear array can have a unique orientation to provide a unique switching direction relative to the remaining optical switching devices within the linear array. Then, multiple linear arrays can be placed adjacent to each other, such as in columns, to form the larger planar array. The larger planar array can also be referred to as a die. Each linear array of the larger planar array or die can be assigned to a specific, individual information port. The number of information ports serviced is dependent upon the number linear arrays provided. The number of linear arrays provided, and hence the number of information ports serviced, can be in the range from thirty-two (32) to two-hundred-fifty-six (256) ports or more, depending upon the application of the planar array or die.